Fuel reformer

ABSTRACT

A reformer ( 5 ) which generates hydrogen-rich reformate gas by causing a catalytic reaction of fuel and air comprises a premixing chamber ( 12 ) for premixing the fuel with the air. High temperature air is supplied to the premixing chamber ( 12 ) from an air intake tube ( 13 ) via an orifice ( 14 ). A fuel injector ( 16 ) injects the fuel into the flow of the high temperature air in the premixing chamber ( 12 ) to generate fuel-air mixture. A homogenizing filter ( 17 ) homogenizes the composition of the fuel-air mixture in the premixing chamber ( 12 ) and supplies a uniform fuel-air mixture to a reforming catalyst ( 11 ).

FIELD OF THE INVENTION

[0001] This invention relates to a reformer for producing hydrogen-richreformate gas from hydrocarbon fuel.

BACKGROUND OF THE INVENTION

[0002] JP2001-180904 published by the Japanese Patent Office in 2001discloses a reformer which produces reformate gas containing a largeamount of hydrogen by causing a reaction of fuel mixture in the presenceof a catalyst. The fuel mixture comprises hydrocarbon fuel such asgasoline or methanol and air as an oxidation agent.

[0003] The reformer is specifically used for producing hydrogen which issupplied to an anode of a fuel cell stack. In the reformer, the fuel isinjected into a premixing chamber by an injector, mixed with air in thepremixing chamber, and lead to the catalyst as a fuel mixture.

SUMMARY OF THE INVENTION

[0004] If the fuel and air are not mixed uniformly, the reformingreaction will also not be performed uniformly when the catalyst invokesthe reaction of the fuel mixture. If the reforming reaction isnon-uniform, the composition of the reformate gas as a result of thereforming reaction will not be uniform.

[0005] In order to ensure the uniformity of the fuel mixture, it may benecessary to increase a distance between the injector and the catalystor provide a supplemental premixing chamber. However, these arrangementsmake the reformer larger in size with a larger heat capacity andincrease the complexity of the construction.

[0006] It is therefore an object of this invention to ensure uniformmixing of fuel and air in the reformer while preventing the aboveinconveniences.

[0007] In order to achieve the above object, this invention provides afuel reformer which generates hydrogen-rich reformate gas by causing areaction of hydrocarbon fuel in the presence of a catalyst, comprising apremixing chamber for mixing the fuel with high temperature air, an airintake tube which supplies the high temperature air to the premixingchamber, an orifice disposed between the air intake tube and thepremixing chamber, the orifice having a smaller cross-sectional areathan a cross-sectional area of the air intake tube, a fuel injectorwhich injects the fuel into the high temperature air, and a homogenizingfilter which homogenizes the flow of a fuel-air mixture generated intothe premixing chamber and leads the fuel-air mixture to the catalyst.

[0008] The details as well as other features and advantages of thisinvention are set forth in the remainder of the specification and areshown in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a schematic diagram of a fuel cell power plant providedwith a reformer according to this invention.

[0010]FIG. 2 is a longitudinal cross-sectional view of the reformer.

[0011]FIG. 3 is a longitudinal cross-sectional view of essential partsof the reformer describing a variation in the thickness of ahomogenizing filter according to this invention.

[0012]FIG. 4 is a diagram describing a characteristic of fuelconcentration of a fuel-air mixture in a premixing chamber with respectto a distance from a center axis thereof.

[0013]FIG. 5 is a longitudinal cross-sectional view of a reformeraccording to a second embodiment of this invention.

[0014]FIG. 6 is a longitudinal cross-sectional view of a reformeraccording to a third embodiment of this invention.

[0015]FIG. 7 is a longitudinal cross-sectional view of a reformeraccording to a fourth embodiment of this invention.

[0016]FIG. 8 is a cross-sectional view of an air intake tube accordingto the fourth embodiment of this invention, taken along a line VIII-VIIIin FIG. 7.

[0017]FIG. 9 is a longitudinal cross-sectional view of essential partsof the reformer according to the second-fourth embodiments of thisinvention, describing a variation in the thickness of the homogenizingfilter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Referring to FIG. 1 of the drawings, a fuel cell power plant 1for a vehicle comprises a fuel cell stack 2, a reformer 5, a carbonmonoxide (CO) removal device 4, an air compressor 3, a combustor 6 and aheat exchanger 7.

[0019] The fuel cell stack 2 is a stacked body of fuel cells whichgenerate electric power by the electrochemical reaction of hydrogen (H₂)provided from the reformer 5 via the CO removal device 4 and oxygen (O₂)provided in the form of air from the air compressor 3 under the presenceof a catalyst.

[0020] Gasoline as a hydrocarbon fuel and air from the air compressorafter being heated by the heat exchanger 7 are supplied to the reformer5.

[0021] The reformer 5 causes a reaction of fuel-air mixture in thepresence of a catalyst to produce reformate gas which mainly containshydrogen. The reformate gas then flows into the CO removal device 4together with air supplied from the air compressor 3.

[0022] In the CO removal device 4, preferential oxidation of carbonmonoxide contained in the reformate gas takes place in the presence of acatalyst. Due to this reaction, the CO concentration of the reformategas is reduced. The reformate gas after its CO concentration has beensufficiently reduced is then supplied to an anode of the fuel cell stack2.

[0023] Hydrogen in the reformate gas supplied to the anode of the fuelcell stack 2 is used for electric power generation by the fuel cellstack 2. The residual gas at the anode is discharged as anode effluent.Since the anode effluent still contains a considerable amount ofhydrogen, it is supplied to the combustor 6 and burned in the combustor6. The combustion gas is supplied to the heat exchanger 7 for heatingair which is supplied from the air compressor 3 to the reformer 5 asdescribed above.

[0024] Next, referring to FIG. 2, the reformer 5 comprises a premixingchamber 12 formed in a cylindrical housing 15, a homogenizing filter 17,a heater 18 and a reforming catalyst 11.

[0025] High temperature air is introduced into the premixing chamber 12from the heat exchanger 7 via an air intake tube 13 formed at an end ofthe housing 15. An orifice 14 for accelerating the air flow inflowinginto the premixing chamber 12 is formed in the intake tube 13.

[0026] The reformer 5 further comprises a fuel injector 16. Gasoline issupplied to the fuel injector 16 as fuel at a constant pressure and thefuel injector 16 injects fuel against the air flow in the premixingchamber 12 to generate a mixture of fuel and air. The injection point ofthe fuel injector 16 is set to be located on the extension of the centeraxis of the orifice 14. The fuel injection direction of the fuelinjector 16 is set such that fuel is injected in the reverse directionof the air flow from the orifice 14 to the premixing chamber 12. A fuelinjector having a wide injection angle is applied for the fuel injector16. A sufficient distance is set between the fuel injection point of thefuel injector 16 and the orifice 14 to prevent the injected fuel frombeing adhered to the wall of the premixing chamber 12.

[0027] The homogenizing filter 17 is disposed at a downstream side ofthe premixing chamber 12 with respect to the flow of fuel-air mixture inthe housing 15. The homogenizing filter 17 is made of a heap of thinmetal fibers or porous ceramic and provided with numerous cellsconnected to each other.

[0028] The heater 18 is an electrically activated heater and disposed inthe homogenizing filter 17.

[0029] In the reforming catalyst 11, a number of passages are delimitedby walls coated with a precious metal catalyst. The fuel-air mixtureflowing through these passages is inevitably in contact with thecatalyst, thereby performing a chemical reaction.

[0030] The cross-sectional area of the homogenizing filter 17 is setequal to that of the reforming catalyst 11. Having the cross-sectionalarea equal to that of the reforming catalyst 11 causes the fuel-airmixture inflowing into the reforming catalyst 11 to disperse evenly,enhance the working efficiency of the reforming catalyst 11 and ensurethe constant composition of the reformate gas which the reformingcatalyst 11 generates.

[0031] The reformate gas thus generated by the reforming catalyst 11 islead to the CO removal device 4 from an outlet 19 formed at another endof the housing 15.

[0032] In the reformer 5, high temperature air spouts out from the airintake tube 13 via the orifice 14 into the premixing chamber 12. Thefuel injector 16 injects fuel towards the flow of this high temperatureair. The injected fuel collides with the high temperature air, mixedwith the air, and vaporized upon receiving heat from the hightemperature air.

[0033] The flow of the fuel-air mixture thus generated then collideswith the homogenizing filter 17 and circulates within the premixingchamber 12 from the centermost part towards outside as shown in FIG. 2.This circulation promotes the mixing of the fuel and air. Mixing of thefuel and air is further promoted by the homogenizing filter 17 when thefuel-mixture passes therethrough.

[0034] Since the catalytic reaction performed in the reforming catalyst11 is an exothermic reaction, the homogenizing filter 17 is heated bythe heat generated by the reforming catalyst 11. The high temperature ofthe homogenizing filter 17 helps to vaporize the fuel in the fuel-airmixture.

[0035] The mixture of the vaporized fuel and high temperature air thuscreated and uniformly mixed together is supplied to the reformingcatalyst 11. Fuel concentration in the mixture is therefore sufficientlyuniform, so the reaction in the reforming catalyst 11 is also performeduniformly at a constant reaction temperature, and the resultantreformate gas maintains a constant preferable composition.

[0036] According to this reformer 5, the fuel concentration of themixture is homogenized without setting a large distance between theinjection point of fuel and the reforming catalyst 11, which can makethe reformer 5 compact in size.

[0037] The heater 18 is activated according to the reforming condition.For example, it is activated when the fuel cell power plant startsoperation, or when large amount of fuel is supplied to the reformer 5according to a large power generation load, so as to vaporize the fuelwhich is not vaporized by the heat of the high temperature air.

[0038] Referring now to FIG. 4, the circulation of the fuel-air mixtureformed in the premixing chamber 12 has a tendency to vary the fuelconcentration of the mixture at an inlet of the homogenizing filter 17such that it becomes high as it approaches towards the center of thecross-section of the premixing chamber 12.

[0039] Therefore, it is preferable that the specifications of thehomogenizing filter 17 are determined to compensate for the increase inthe fuel concentration in the centermost part of the inlet of thehomogenizing filter 17.

[0040] Specifically, if the thickness of the homogenizing filter 17 isconstant, it is preferable to set the fineness of the homogenizingfilter 17 to be different according to a distance from the center of thehomogenizing filter 17 towards its outer periphery. In the centermostpart of the filter 17, the fineness should be high and it should becomelower as the distance from the center of the filter 17 increases.

[0041] If the fineness of the homogenizing filter 17 is constant, thethickness of the homogenizing filter 17 should be changed, i.e., itshould decrease as the distance from the center of the homogenizingfilter 17 increases as shown in FIG. 3.

[0042] By the above arrangement with respect to the specification of thehomogenizing filter 17, inlet resistance of the fuel-air mixture intothe homogenizing filter 17 is larger at the centermost part and smallerat an outer peripheral part. This difference in the inlet resistancecompensates for the difference in the fuel concentration of the fuel-airmixture and evens out the fuel concentration of the fuel-air mixturewhen it is lead into the reforming catalyst 11.

[0043] Next, referring to FIG. 5, a second embodiment of this inventionwith respect to the construction of the reformer 5 will be described.

[0044] According to this embodiment, the fuel injector 16 is disposed inthe air intake tube 13, not in the premixing chamber as in the firstembodiment.

[0045] The fuel injector 16 is arranged to inject fuel in the reversedirection to the flow of the high temperature air in the air intake tube13. In the downstream of the orifice 14, an interrupting plate 23 issupported by supports 20 which are fixed to the housing 15. Theinterrupting plate 23 is in the shape of cone the top end of which isdirected against the orifice 14.

[0046] The fuel injected from the fuel injector 16 is mixed with thehigh temperature air flowing through the air intake tube 13 and forms afuel-air mixture. The flow of this fuel-air mixture is then acceleratedby the orifice 14 and mixing of the fuel and air is further promoted.Since the fuel injector 16 is disposed in the air intake tube 13 in thisembodiment, the distance between the fuel injection point and thereforming catalyst 11 can be set larger than that of the firstembodiment. Accordingly, the period from the fuel injection until thecatalytic reaction of the injected fuel can be increased. The mixing ofthe fuel and air can be fully performed during this time period.

[0047] The interrupting plate 23 interrupts the flow of the fuel-airmixture spouted out from the orifice 14 into the premixing chamber 12,thereby dispersing the fuel-air mixture in the premixing chamber 12. Anumber of eddies are formed at a downstream side of the interruptingplate 23 and these eddies further promote the mixing of the fuel andair.

[0048] According to this embodiment, therefore, the concentration of thefuel in the fuel-air mixture at the inlet of the reforming catalyst 11can further be homogenized.

[0049] Next, referring to FIG. 6, a third embodiment of this inventionwith respect to the construction of the reformer 5 will be described.

[0050] According to this embodiment, a swirl generator 21 is provided inthe orifice 14 instead of the interrupting plate 23 of the secondembodiment. The swirl generator 21 exerts a revolving force onto theflow of the fuel-air mixture which passes through the orifice 14 so asto form a swirl of the fuel-air mixture around the center axis of thehousing 15 in the premixing chamber 12. This swirl in association withthe inlet resistance of the homogenizing filter 17 causes a circulationof the mixture in the premixing chamber 12 in the direction from theouter periphery of the premixing chamber towards the centermost partthereof at the inlet of the homogenizing filter 17 as illustrated in thefigure. This circulation further promotes mixing of the fuel and air inthe premixing chamber 12.

[0051] Next, referring to FIGS. 7 and 8, a fourth embodiment of thisinvention with respect to the construction of the reformer 5 will bedescribed.

[0052] Referring to FIG. 7, according to this embodiment, a swirlgenerator 22 is installed in the air intake tube 13 upstream of the fuelinjector 16 instead of the swirl generator 21 of the third embodiment.

[0053] Referring to FIG. 8, the fuel injector 16 is arranged to injectfuel along a tangent line of the circular cross-section of the airintake tube 13 such that the injected fuel joins the swirl of the hightemperature air towards the orifice 14. When the resultant fuel-airmixture ejected from the orifice 14 into the premixing chamber 12, itdisperses along the cylindrical wall of the premixing chamber 12 due tothe centrifugal force of the swirl. This dispersal of the fuel-airmixture in association with the inlet resistance of the homogenizingfilter 17 causes a circulation of the fuel-air mixture similar to thatgenerated by the third embodiment. According to this embodiment also,mixing of the fuel and air in the premixing chamber 12 is enhanced.

[0054] In the second-fourth embodiments in which the fuel injector 16 isdisposed in the air intake tube 13, circulation of the fuel-air mixturepromoted by the interrupting plate 23 or swirl generators 21, 22 takesplace in the premixing chamber 12. This circulation of the fuel-airmixture has a tendency to vary the fuel concentration of the fuel-airmixture at the inlet of the homogenizing filter 17. In theseembodiments, unlike the case of the first embodiment, the fuelconcentration is higher at an outer periphery of the premixing chamber12 with respect to the centermost part thereof.

[0055] Accordingly, in these embodiments, it is preferable to vary thespecification of the homogenizing filter 17 such that it can cancel outthe variation in the fuel concentration of the fuel-air mixture at theinlet of the homogenizing filter 17.

[0056] Specifically, if the thickness of the homogenizing filter 17 isconstant, the fineness of the homogenizing filter 17 should increase asthe distance from the center axis towards the outer periphery increases.If the fineness of the homogenizing filter 17 is constant at any part,the thickness of the homogenizing filter 17 should increase as thedistance from the center axis in the radial direction increases as shownin FIG. 9.

[0057] In any of the above cases, the inlet resistance to thehomogenizing filter 17 is larger at the outer peripheral part of thepremixing chamber 12 and smaller at the centermost part thereof. Thisdifference in the inlet resistance compensates for the difference in thefuel concentration of the fuel-air mixture and evens out the fuelconcentration of the fuel-air mixture introduced into the reformingcatalyst 11.

[0058] The contents of Tokugan 2002-106642, with a filing date of Apr.9, 2002 in Japan, are hereby incorporated by reference.

[0059] Although the invention has been described above by reference tocertain embodiments of the invention, the invention is not limited tothe embodiments described above. Modifications and variations of theembodiments described above will occur to those skilled in the art, inlight of the above teachings.

[0060] The embodiments of this invention in which an exclusive propertyor privilege is claimed are defined as follows:

What is claimed is:
 1. A fuel reformer which generates hydrogen-richreformate gas by causing a reaction of hydrocarbon fuel in the presenceof a catalyst, comprising: a premixing chamber for mixing the fuel withhigh temperature air; an air intake tube which supplies the hightemperature air to the premixing chamber; an orifice disposed betweenthe air intake tube and the premixing chamber, the orifice having asmaller cross-sectional area than a cross-sectional area of the airintake tube; a fuel injector which injects the fuel into the hightemperature air; and a homogenizing filter which homogenizes the flow ofa fuel-air mixture generated in the premixing chamber and leads thefuel-air mixture to the catalyst.
 2. The fuel reformer as defined inclaim 1, wherein a cross-sectional area of the homogenizing filter isset equal to a cross-sectional area of the catalyst.
 3. The fuelreformer as defined in claim 1, wherein the homogenizing filter is madeof any one of thin metal fibers and porous ceramic.
 4. The fuel reformeras defined in claim 3, wherein the homogenizing filter is formed to havea constant thickness in the direction of the flow of the fuel-airmixture, and a varying fineness according to a radial distance from acenter axis of the homogenizing filter.
 5. The fuel reformer as definedin claim 3, wherein the homogenizing filter is formed to have a constantfineness and a varying thickness in the direction of the flow of thefuel-air mixture according to a radial distance from a center axis ofthe homogenizing filter.
 6. The fuel reformer as defined in claim 1,wherein the homogenizing filter comprises a heater which heats thefuel-air mixture flowing through the homogenizing filter.
 7. The fuelreformer as defined in claim 1, wherein the fuel injector comprises afuel injector which injects the fuel against a flow of the hightemperature air which is flowing from the orifice into the premixingchamber.
 8. The fuel reformer as defined in claim 1, wherein the fuelinjector comprises a fuel injector which injects the fuel towards thehigh temperature air flowing through the air intake tube.
 9. The fuelreformer as defined in claim 8, wherein the fuel reformer furthercomprises an interrupting plate which redirects a flow of the fuel-airmixture which is flowing from the orifice into the premixing chamber,towards an outer periphery of the premixing chamber.
 10. The fuelreformer as defined in claim 9, wherein the interrupting plate isdisposed coaxially with the orifice and is formed in a shape of a coneof which a projecting end is directed to the orifice.
 11. The fuelreformer as defined in claim 8, wherein the fuel reformer furthercomprises a swirl generator which exerts a revolving force on a flow ofthe fuel-air mixture in the orifice.
 12. The fuel reformer as defined inclaim 8, wherein the fuel reformer further comprises a swirl generatorwhich is disposed in the air intake tube and exerts a revolving force ona flow of the high temperature air in the air intake tube, the fuelinjector is disposed downstream of the swirl generator in the air intaketube and arranged to inject the fuel along a tangent line of arevolution of the high temperature air.